In recent years, artificial leather which is a natural leather substitute has been widely used in the field of garments, shoe uppers, handbags, gloves, sports equipment, and upholstery for use in furniture and automotive seats and trim applications. The property requirements for artificial leathers vary depending on the application and kind of fabrication. Generally, artificial leathers are coated fabrics. The production of coated fabrics is well known; one or more coating-agent is applied to a fabric substrate using either a direct coating process or a transfer process.
Direct processes include the application of a coating-agent as a solution or suspension in an organic solvent such as dimethylformamide (DMF), tetrahydrofuran (THF), or dimethylsulfoxide (DMSO). The coating-agent is applied to and impregnates the surface of a fabric. Suitable fabrics can be woven, non-woven, knitted, twilled, sweating, or the like. The impregnated fabric is heated, the coating-agent cures, and the solvent evaporated. However, this process provides a flat non-attractive surface lacking any three-dimensional “grain-like” feeling. Furthermore, the evaporation of the solvents creates environmentally undesirable volatile organic compounds (VOCs).
A common direct transfer process utilizes a release paper sometimes known as film casting paper and is referred to as a paper transfer process. The use of such release paper is an established procedure. It has a release surface, smooth or carrying a negative or reverse of a pastern (emboss) required in the final artificial leather. The release paper is usually used by extruding onto the release surface a coating-agent which will cure when heated to form the artificial leather surface. The coated release paper is then laminated, typically by heat and/or pressure, to a base fabric. The polymer impregnates the fabric and after cooling the release paper is stripped from the surface polymer revealing a smooth surface or, where present, the positive of the emboss.
A common type of coating-agent is a plastisol or organosol. Plastisol or organosol generally refer to dispersions of fine plastic particles in softeners, sometimes referred to as plasticizers, which harden or gelate when heated to high temperatures. The plastic particles typically comprise polyvinyl chloride-vinyl acetate copolymer (PVC/PVAc), polymethyl methacrylate (PMMA), and polyalkyl methacrylate (PAMA) such as polymethyl methacrylate copolymers, and most commonly polyvinyl chloride (PVC). Phthalic acid esters are most commonly used softeners. Plastisol or organosol may further contain other ingredients depending on the specific end-use application.
While plastisol and organosol coating-agents have enjoyed wide-scale use, they suffer from many draw backs, especially in interior automotive applications. For instance, their heat properties are marginal and, over time, the softeners bleed resulting in a reduction of the artificial leather's properties, such as decreased durability and strength. Further, the softeners may cause undesirable odors as well as a film build-up on the inside of the windows.
There are other polymeric resins used as coating-agents, such as amino acid resins, nylon resins, and most frequently polyurethane resins. While the use of these resins eliminate the problems created from the bleeding of the plasticizers used in PVC plastisols, the artificial leather produced from these resins have inferior surface strength and it is technically difficult to achieve the desired thick feel to the artificial leather.
Thus, there is a need, especially by the automobile manufacturers, for an improved polymer composition and process to produce artificial leather for automotive seat and interior trim applications; in particularly, a polymer composition that easily lends itself for use in paper transfer processes while reducing, or preferably eliminating, VOCs, provides improved heat properties, reduces or eliminates bleeding, and exhibits good long term physical properties in the final artificial leather application.